Semiconductor chips are manufactured by processing a wafer in respective semiconductor processing chambers. Such processing may include chemical vapor deposition (CVD), physical vapor deposition (PVD), or any other processing which is known in the art. The processing chamber used for each process is designed for purposes of carrying out the respective process. The process of depositing layers on a semiconductor wafer substrate usually involves placing the substrate on a silicon carbide coated graphite susceptor in a thermal reactor chamber and holding the wafer within a stream of a reactant gas flowing across the surface of a wafer. The thermal reactor may be heated by external lamps which pass infra-red radiation into the reactor chamber through heating ports. The heating ports are typically positioned both above and below the susceptor. The heating ports are covered by quartz windows that are transparent to the infra-red radiation. The susceptor positions and rotates the wafer during the deposition process. A pyrometer aimed at the back of the susceptor is generally used to detect the temperature of the susceptor during processing and to serve as an input to a controller that controls power to the external lamps.
During processing, the deposition film is also deposited on the surfaces of other components within the reactor chamber, including the susceptor. For example, during a high temperature nitride process, silicon nitride is deposited on the internal walls of the chamber and also on the silicon carbide coated graphite susceptor. As the deposition layer thickens the silicon nitride may flake and introduce unwanted particulates into the processing chamber. In addition, the emissivity of the susceptor will change as a result of the deposited silicon nitride film. As the emissivity changes, the ability of the pyrometer to accurately monitor the temperature of the susceptor is compromised thus limiting the precision at which a deposition layer may be deposited. For these reasons, an in-situ etch cleaning process is periodically used to etch the silicon nitride film from the susceptor and chamber walls, including the quartz windows. Typically a fluorine containing gas (NF.sub.3) is used to clean the deposited film from the surface of the susceptor. Since it is difficult to precisely control and monitor the etch rate of the deposited film, it is not uncommon for the silicon carbide coating of the susceptor to be etched during the cleaning process. After a portion of the silicon carbide coating is fully removed, the graphite susceptor will itself be subject to attack by the etchant.
Removal of the silicon carbide coating not only exposes the graphite susceptor to the etchant gas, but also affects the emissivity of the susceptor. This, in turn, affects the thermal characteristics of the susceptor making it more difficult to precisely control the temperature of the wafer during processing. Moreover, etching of the graphite body reduces the structural integrity of the susceptor itself.